The invention relates to a pump of vane type, and in particular, to a variable displacement pump of vane type capable of changing the fluid discharge therefrom.
A vane pump of unbalanced pressure type is known in the prior art which includes a truly circular rotor and a truly circular cam ring. By adjusting the eccentricity between the axis of the rotor and the axis of the cam ring, the fluid discharge can be readily changed, and a variety of variable displacement vane pumps have been in practical use. However, in a vane pump of balanced pressure type which defines a pair of pump sections at locations which are symmetrical with respect to the axis, the relative position of the rotor and the cam rimg is fixed, and hence it is not a simple matter to provide a variable displacement arrangement. While such attempt has been made in the prior art and several vane pumps of balanced pressure type have been proposed which provide a variable displacement, the known arrangements are complex in a construction or exhibit an increased size, resulting in an expensive structure, which stood in the way to their practical use.